Bring a large pot of heavily salted water to a rolling boil. Add the spaghetti and cook according to package directions until al dente. Before draining, reserve 1.5 cups of the starchy pasta water. Drain the spaghetti and set aside.

While the pasta cooks, heat the extra virgin olive oil in a large skillet or deep pan over medium-low heat. Add the thinly sliced garlic and red pepper flakes. Cook gently, stirring occasionally, for 5-7 minutes, or until the garlic is fragrant, softened, and just barely golden. Be careful not to burn the garlic, as it will become bitter.

Add the drained spaghetti directly into the skillet with the garlic oil. Pour in 1 cup of the reserved pasta water. Increase the heat to medium-high and toss vigorously with tongs, allowing the sauce to emulsify and coat the spaghetti. Cook for 2-3 minutes, adding more pasta water a little at a time if the sauce seems too dry, until a glossy, rich sauce forms.

Stir in the chopped fresh parsley, salt, and black pepper. Toss well to combine. Taste and adjust seasoning as needed. Serve immediately, garnished with extra fresh parsley and a sprinkle of freshly grated Parmesan cheese, if desired.